In the known hybrid drives addressed here, an internal combustion engine is combined with at least two electric motors/generators, so that a plurality of drive sources for the vehicle are available. According to requirements specified by a vehicle driver, the drive sources may optionally feed their driving torque into a power train of the vehicle. This results in various drive configuration possibilities depending on the driving situations, which drive configurations are used to improve ride comfort and to reduce energy use, as well as to reduce pollutant emission.
In hybrid drives for vehicles, serial arrangements, parallel arrangements and mixed arrangements of internal combustion engine and electric motors/generators are known. Depending on the arrangement, the electric motors/generators may be connected to the power train of the internal combustion engine directly or indirectly. For the mechanical linkage of the internal combustion engine and/or the electric motors/generators, it is known to arrange them in such a way that they are mechanically linkable with each other using a transmission, e.g., a planetary transmission, or the like, and clutches.
Optimum implementation of a driver's desired driving power from the hybrid drive requires coordinated activation of the propulsion engines of the hybrid drive, which is accomplished by a device known as an engine control unit. In every driving situation of the vehicle, the driver's wish must be satisfied in an optimum way with the resources provided by the vehicle. Known operating strategies for hybrid drives define an optimized operating point for the internal combustion engine, depending on specific input values such as driving power demand, vehicle velocity, roadway gradient, and the like. An effort is made to operate the internal combustion engine outside of the least efficient partial load range, insofar as possible, and to shut it off at minimum desired power output levels, if appropriate. In these cases, the at least one electric motor/generator takes over the propulsion of the vehicle. It is also known to control the internal combustion engine along an optimum fuel consumption characteristic curve. A disadvantage of these known operating strategies is that the efficiencies of the electric propulsion engines and the effects of the operating behavior of the electric propulsion engines on electric energy storage devices (batteries) are ignored.